Wes went out of his way to avoid his Mom's new husband...and the new life they were building together.

A new start financed by Nancy's handsome divorce settlement.

And the new husband came with a package deal. Along with him, Nancy was getting his young friend Efren Gallegos, too. A kind of sidekick of Dan's–a guy who Dan–and now Nancy–were taking under their wings.

He'd work with Dan on some business ventures, and help Nancy around the house...

Miriam Gaede: And of course, Nancy looks after everybody. And they made room for him to move in.

And six months into the new marriage, Dan, Nancy and their friend Efren decided to take a fishing trip over Memorial Day weekend.

Dan was familiar with the canyons around Salida, Colorado, about three hours from Denver.

So off they went. And even though her family says Nancy had never been one for lacing up the hiking boots–far from it–Dan would later recall that on Sunday morning the three took a hike on the old gold-miners trails...out past the ghost town of St. Elmo.

Later, they stopped at a fishing spot on Chalk Creek just below the ghost town.

Wes Linville: I got a phone call from my brother Ben. He said, “There was an accident. I need you to get down to your brother’s house."

Wes raced to see his oldest brother Matt in person…

Matt Linville: And he opens the door and shuts it right behind him. And his eyes are as big as saucers.

Wes Linville: He said, you know, you look like you've seen a ghost. And–and I just started crying, and, you know, I said, "Well, mom's dead." And–then he just started crying. And–it was–probably the hardest moment in my life. (cries)

In the days ahead, Nancy's family–her children, siblings, even her ex–gathered to comfort each other.

Her dad, Bill Gaede:

Bill Gaede: We were in the fog, we just couldn't make sense of it, you know.

Miriam Gaede: It was just like a blur.

Wes Linville: They started telling us, you know, what had happened. And they said that they were out fishing and that, you know, she fell down the side into a river. She didn't have the greatest balance. She didn't have the greatest feet. I can see her falling.

And not all that unusual a death.

Chaffee County where Nancy died gets its fair share of fatal accidents, hikers, climbers. River accidents like Nancy's.

But Nancy's sons look back at their mother's funeral and remember a bizarre Dan Mason.

Wes Linville: There was just him going, "Oh–oh."(fake moan) like if you wanted, you know, to watch that, I'd probably turn on a soap opera.

And after the service, the brothers say Dan refused to answer questions about exactly how their mother had died...

Matt Linville: He said he was uncomfortable talking about it. He did not wanna talk about it at all.

But the sons say he did want to talk about her estate. Not talk actually. He passed each of the boys an envelope with a note inside. None of them kept the letter, but recall it went something like this...

Wes Linville: "I'm grieving right now and all this stuff was our stuff. And I'd appreciate it if you guys would leave me alone."

Dennis Murphy: Nothing sentimental about your mom and how much he loved her and–

Wes Linville: No. It was, “Leave me alone and you'll get your stuff in due time.”

As it turns out, the boys would see very little of their mother's estate.

Nancy had two life insurance policies–Dan collected a little more than 150 thousand dollars, while her three sons split 54 thousand dollars among them.

And, just a month before her death, Nancy had signed this new will leaving everything else–the family home, jewelry, and whatever cash was left from her divorce settlement–to Dan.

The will even went on to cite each son individually, saying they were specifically NOT provided for.

It appears that Nancy signed the will, and the family didn't challenge it in court, but to the kids, it stunk to high heaven.

Matt Linville: With new people getting married, I'm sure she would have changed her will but never taken out her kids, never specifically naming her kids out of the will and our names misspelled on top of that.

No one wanted to say it, but the thought–nothing more–was undeniably there: Their mother, who they say didn't fish...who was afraid of rushing water...

Wes Linville: Somebody in front of me said, "You know, what if it wasn't an accident?"

Not an accident?

Maybe things hadn't been so blissful for the second-time-around newlyweds...perhaps three under a roof in a new marriage had been getting a little claustrophobic?

As Nancy's family tells it, not long before the fatal fishing trip, Dan had gotten a sharp message from his new wife concerning their young friend living in the basement.

Matt Linville: It wasn't a popular subject among the family to talk about because–you don't believe it was not an accident–because–then what?

Well then you'd need to involve the sheriff's office down in Chaffee County.

That's where undersheriff Pinkston was having a rethink of his own as he looked over the file on that accident out at chalk creek.

Something seemed not quite right...

Nancy had been gone for four-months and her mother Miriam refused to believe her daughter's death had been anything but what the county coroner had ruled–an accident.

She'd apparently fallen off a rocky ledge while fishing a fast-moving mountain creek with her new husband Dan...

Miriam Gaede: We didn't like him very well. But, we believed his story.

Dennis Murphy: Is he staying in your life, or is he gone?

Miriam Gaede: Oh, no. He wanted nothing to do with us.

All Miriam says she wanted from Dan were a few family heirlooms, pieces that had belonged to her mother.

But Dan fired off a letter to his in-laws reminding them that, "My own life was almost lost on that day!" and wondering if the family thought "tangible goods were more important than the demise of my wife."

Miriam Gaede: There was all brand new furniture, beautiful furniture. Nancy had never had new furniture. There were all kinds of things on the walls. Like masks and swords. And there was a big bar set up. There was no sign of her anywhere.

Wes did end up hauling out the furniture they'd come for...

But as Miriam surveyed the home that she says had been cooly scrubbed of any trace of her daughter's existence, the following words spilled out of her mouth:

Bill Gaede: She said, "You shoved her off of that cliff, didn't you?" "Well you know me better than that," he says.

Dennis Murphy: You confronted him directly?

Mariam Gaede: Oh, definitely.

Dennis Murphy: How long had these suspicions been taking root?

Miriam Gaede: It just, right boom, right then.

Miriam Gaede: That was when the light came on. When we stepped in that house that day, everything changed.

But they didn't have much to grab onto, just their overwhelming sadness and a devastating hunch of foul play.

Three-hours south, in the Chaffee County Sheriff's office, the same flickering thought–something's not right here–had been chewing away at the Undersheriff.

Keith Pinkston had been off-duty the day of the accident. A week later he'd decided to take another look at the paperwork on the case.

He had a look and agreed that the story told creekside that day didn't add up.

Rob Martellaro: It just was different from how it was explained, very different for me

They grumbled privately about the lack of good investigating that should have been done right away but wasn't. The arriving deputy–who was later fired–hadn't even interviewed or gotten the phone number of the good Samaritans on the ATV, the couple who got to the creek even before the EMT's.

Judy Cleveland: From the very beginning, I–didn't feel right about the situation.

Lynn Cleveland: Somethin' was wrong that day.

No one had asked them at the time but it turned out, Lynn and Judy Cleveland had been bothered by a lot of things they took in that day...

For starters, they thought it was strange that Dan and Efren had driven off together to look for help... neither had stayed behind with the critically injured woman. You'd think one of them would.

What's more, they say both men were wearing jackets, and yet they'd left Nancy uncovered–with one leg still submerged in the roaring creek.

Judy Cleveland: I couldn't imagine leaving a loved one by the side of the creek with their foot hanging. Just didn't seem logical.

And there was something else that struck them–and investigators–as suspicious.

They had encountered the men several miles up this bumpy back road.

But when they got to the accident site, the Clevelands realized they were just spitting distance from St. Elmo–the ghost town that on a holiday weekend was abuzz with tourists.

So why had Dan and Efren made a left turn away from the creek and driven several miles up a washboard 4-wheelers' path, when–if they'd gone the other way–the road up the hill could take them into St. Elmo and to help in about 45 seconds?

Rob Martellaro: It's very close.

Dennis Murphy: Maybe they don’t have maps, maybe they don’t know the area? Here's the road and we'll go left instead of right.

Keith Pinkston: Could be possible, but I don’t think it is because they'd just been through St. Elmo.

Rob Martellaro: And in fact, based on their story–they were by there that morning. So they had to know.

And there was one more thing they noticed that seemed to defy common sense.

According to the men's story, Dan and Efren were fishing downstream when Nancy fell...

But no one at the scene reported seeing fishing gear on the ground in this spot...

The Clevelands, however, told investigators that when they arrived they saw Dan's SUV was neatly packed with fishing rods and tackle boxes in the back...

Dennis Murphy: So you have to believe what? That they had this horrible thing with Nancy and then it's, "Oh, we gotta pack up–

Rob Martellaro: Yeah, let's get our stuff packed. Let's leave her.

Dennis Murphy: Does that make sense, any of that?

Rob Martellaro: When you investigate, you try to be objective going in to it to see. But–it doesn't make sense. None of it does.

Growing suspicions. To put the story of a fatal fall to a real test, a team of sheriffs’ investigators later staged an accident recreation–dropping a mannequin Nancy's size into the creek from where she allegedly slipped, and tracking its flow to the spot about 70 yards downstream where the men say they pulled her ashore.

To Pinkston, the results were telling.

Keith Pinkston: When we did our recreation with the mannequin, she would have never gotten past this spot right here.

Dennis Murphy: You would have found her body right there?

Keith Pinkston: She would have been right here. Or she would have been sucked under the rocks right there.

The scene didn't look right, and now Chafee County investigators were contacting Nancy's family for more background. Into the case file went their stories about Dan spending Nancy's estate...what they thought was his weird behavior...And their belief that Nancy never would have been fishing alone on that ledge in the first place.

The questions were piling up: Had it been an accident...or something else?

Investigators from the Chaffee County's Sherriffs department thought they were building a strong case for murder against Dan Mason and his friend Efren Gallegos.

Along with the holes in the story the men told about what happened that day at the creek, the lawmen thought they'd uncovered a pretty compelling motive for wanting Nancy Mason gone...a classic one:

RobMartellaro: Dan Mason–made a benefit from–what happened.

Dennis Murphy: This is money?

Rob Martellaro: This is money.

I would say roughly $300,000 when it was all said and done. A good chunk of change.

In January of 2005, police served a search warrant at the home where Dan and Nancy had lived.

On computers there they found evidence of internet searches for information on dealing with grief, losing a spouse.

But the hard drives revealed other topics of apparent interest–escort services and prostitution...

And two weeks before Nancy died, police say yahoo searches had been performed for "people-plus-poison" and "silent weapons".

The search of the home also turned up what investigators thought could be a smoking gun–a document cops called a "script."

On a bedroom nightstand they found a one page narrative written from Efren's point-of-view. It outlined the events–as they'd already been told–of the day Nancy died.

To investigators it looked like a sure sign the men were making an effort to keep their stories straight.

But in Colorado, and just about everywhere else, investigations don't result in arrests until the district attorney gives a case the go-ahead. In Chaffee County, the prosecutor in the D.A.'s office making that call was not convinced the sheriff's men had the goods.

Keith Pinkston: We explained to him everything we had and they told us we needed more we didn't have enough.

After all, there wasn't a shred of physical evidence to present to a jury–no forensics of any kind to indicate a murder took place.

And remember, Nancy's body had been cremated–the autopsy done at the time concluded her injuries were consistent with an accidental death.

Keith Pinkston: We went back to the drawing board, we got more, what we felt was more...

So in the months–and as it would turn out years–to come, the sheriff's investigators continued digging, bringing each new tidbit to the attention of the DA.

They kept tabs on the men who by then had left Colorado for Texas, Dan Mason's native state.

And the detectives talked to anyone they could find who knew Dan...a story told by this woman, Janet Kiddy, merited special attention:

Dennis Murphy: It's a long time ago, you don't have a body, you don’t have a lot of things you'd like to talk about in opening arguments if you're a DA.

Rob Martellaro: Everyday in America there are cases like this and they move forward. Some are successful, some are not.

Keith Pinkston: To be honest with you, Dennis, if–I could convince myself at any point during this investigation this was an accident, it would've made my life a lot easier.

I cannot convince myself it's an accident. And I feel my own duty to pursue it now as a homicide.

And pursue it they did, attempting a creative end run around their DA.

They took their case file with its 95 bullet-pointed red flags to the County Coroner–the very official who had deemed Nancy's death an accident back when–and convinced him to give it a hard, second look.

The coroner agreed, and in May of this year convened a public hearing on the evidence–a rare procedure in Colorado called a Coroner's inquest.

Dennis Murphy: What was your understanding of what the goal of a coroner's inquest was in your case?

Bill Gaede: To change the death certificate from accident to homicide, or unknown.

A panel of six jurors was seated–their job to render a verdict on how Nancy died.

There it was in black and white–a new death certificate declaring Nancy Mason the victim of a homicide.

Miriam Gaede: So, we went away thinking, we're going to get some justice for Nancy.

Dennis Murphy: Good news for you and the family?

Wes Linville: Great news.

Arrest warrants for her husband Dan and his friend Efren Gallegos were issued–and police were dispatched to the Dallas, Texas apartment complex where the two men had been living.

Rob Martellaro: They went and picked Efren up immediately, but couldn't find Dan.

As the Texas search for Dan continued, Nancy's family made the three-hour drive to Salida to see Efren who'd been extradited back to Colorado. There, Nancy's mother confronted him at his court appearance.

Miriam Gaede: I said, "Efren, Nancy was good to you, and you killed her," and he just kept his head down. He never looked up.

But it was Efren–and by extension Dan–who would prevail in court that day.

Despite the jury's ruling that Nancy's death had been a homicide, the DA came to court and told a judge...there's no case here.

District Attorney Thom LeDoux: I believe that there's not evidence to file criminal charges at this time.

Thom LeDoux has been the elected DA in Chaffee County since just January, but he holds the exact same position on the case that the prosecutor's office has maintained for years.

Dennis Murphy: It's your core belief that the case as it exists now is a loser.

Thom LeDoux: It's not about winning or losing. There's not enough evidence to prove that Nancy Mason died as a result of–as–of a criminal act.

For starters, the DA points out that while the jurors may have believed Nancy was murdered, the panel was undecided on the question of what actually killed her...Was it a broken neck? Or maybe a drowning? Perhaps a blow to the head? They couldn't say. And there were no remains to reexamine.

Thom LeDoux: Deciding how she died–is an important aspect of proving who killed her and–and how they killed her.

And where the investigators see suspicious behavior, the DA sees plausible explanations.

The men left Nancy alone by the Creek because–they say–neither knew CPR. What could they have done for her?

And driving the wrong way to look for help? Maybe that's because they were distraught, disoriented.

Thom LeDoux: This was their explanation. We were–we didn't know exactly which way to go.

As for the money motive? The DA says it could be argued that Nancy was actually worth more to Dan Mason alive then dead. She was still owed another 75 thousand dollars cash from the divorce settlement, and they were apparently living off her nursing salary and $3500-a-month alimony.

What's more, the DA says a lot of the persuasive evidence the coroner's jury heard wouldn't be admissible in a criminal trial–things like stories about Dan's troubled first marriage.
Video: Nancy Mason’s last moments (on this page)

But even if he could put Dan's ex-wife on the stand, the DA says the fact that they were married for 12-years might play to the defenses hand.

Thom LeDoux: It's not as if there is simply a pattern of marrying individuals for their money, and then–attempting to kill them. None of the other women that–Mr. mason has been married to have died.

LeDoux also points out that, as with any cold case, memories can become unreliable. The Clevelands, for example, weren't even interviewed for months...and now 5 years have gone by.

Dennis Murphy: Did you guys scream?

As for our entirely unscientific test that showed it would be hard to hear a scream over the rushing water? Well he says members of the DA's office came to a different conclusion.

Thom LeDoux: The individuals–all relayed to me that it was loud but you could hear someone scream.

Dennis Murphy: Have you been up to the scene?

Thom LeDoux: I have not been there.

Thom LeDoux: I have relied on the on-scene observations of the members of my staff.

And finally, that so-called smoking gun document investigators found in Dan and Efren's house, outling the event of that day?

Wasn't that a sign the two men were trying to keep their stories straight...?

Dennis Murphy: What about the script of what happened?

Thom LeDoux: When Dan Mason was questioned about the script, he freely admitted he had authored the script. And he indicated that it was part of a therapeutic–suggestion

Dennis Murphy: Therapeutic?

Thom LeDoux: I–I'm not a therapist.

Dennis Murphy: Jurors would look at that and say, "That stinks. Why do these two guys have a script, a common story that they've worked out?"

Thom LeDoux: I'm not suggesting that there isn't something strange about the script.

It does not prove conclusively that Dan Mason and Efren Gallegos murdered Nancy Mason on May 30th, 2004.

In other words... Lots of smoke maybe. But not enough legal fire.

Thom LeDoux: We have a legal and ethical responsibility only to carry forward cases that we believe there was a crime committed, and that we can prove who committed the crime. You don't just roll the dice to see–you know, to see if something will stick.

So after spending 10 days in police custody, Efren Gallegos was let go. The search for Dan Mason...was called off.

We went looking for him, to find out what he had to say about that day on Chalk Creek.

After five years of investigating, five years of smoldering suspicions, the Chaffee County DA added all the "what if’s"…and decided NOT to charge Dan Mason and his friend for the murder of Nancy Mason.

In the end, he says it wasn't even a close call.

Thom LeDoux: To be honest with you, it really wasn't a very difficult decision to make.

To say that Nancy's family is furious with him would be understating the case.

As for the man at the center of the sheriff's investigation – Dan Mason – where had he gone and what did he think about the uproar he'd left behind in Chaffee County, Colorado?

He'd been a wanted man for just a few days in late spring, remember, but police had lost track of him.

Dateline learned that just about the time the cold case was heating up again in Colorado, Dan Mason moved from Dallas to San Antonio, where this woman–Gloria Donovan–tells us she was introduced to him as "Dan Reed."

She knew nothing about the investigation in Colorado when they met, but says she didn't trust him from the get-go...

Gloria Donovan: It was everything. His whole behavior. It was all fake and phony and deliberate.

Dan is currently dating one of Gloria's close friends, someone she describes as both wealthy and naive.

Gloria Donovan: He wanted to marry her right away, and have her go to Las Vegas.

We, of course, wanted to talk to Dan, ask him about his wife's death...his actions on that day and in the months that followed.

So we went to the home where he's apparently living with his new female companion. She answered the door and told us Dan wasn't there.

But it turned out he was home. And minutes later on the phone he said we could come in for an interview–in exchange for money.

As proof of innocence, Dan Mason cites the DA's refusal to prosecute and the coroner's original determination that Nancy's death was accidental.

And he says he has repeatedly answered questions about what happened that day...and has never changed his account of events.

Dan Mason's "story" also accuses the Chaffee County Sherriff's Department of leaking false information about him to the media...and says investigators attempted to bribe Efren Gallegos to "make up a story" against him–something the sherriff's department denies.

We tried to contact Efren Gallegos, but he declined to comment on the case.

But there is one more card to turn over. The case isn't dead yet, but it's a legal longshot. In a highly unusual move, the sheriff and county coroner had asked a Colorado judge to appoint a special prosecutor to try the two men for murder.

Just today, they withdrew that request, but say they plan to file it again after refining their legal strategy.

Keith Pinkston: At least we can go to the Gaede family and tell them that we did everything we could. We took it as far as we could. And we gave it everything we had for Nancy and for them.

Matt Linville: She was smiling...

Bill Gaede: She was pretty happy there.

For now, Nancy's family is left with her scrapbooks to refresh their memories...

Wes Linville: There's not a day that goes by that, you know, something doesn't remind me of her you never–you never know what you have until it's gone.

Gone with a scream and a headlong plunge into a furious rocky creek. Or maybe it happened another way? That's the mystery of it all that's just eating some people up. The whitewater of Chalk Creek may roar, but no one can make out its words.